The invention relates generally to nucleic acids and polypeptides and in particular to the identification of psychotropic agents using differential gene expression.
Neuroleptics are agents that are used to treat psychotic disorders such as schizophrenia. They can cause side effects that cause disruptions of the motor system.
In humans, they further reduce initiative and interest in environmental stimuli, and suppress manifestations of emotion. An important neuroleptic agent is haloperidol, a member of the butyrophenone (phenylbutylpiperidine) class of heterocyclic antipsychotic agents used in the treatment of schizophrenia. Other members of the butyrophenone class include droperidol, a short-acting highly sedative compound used for anaesthesia induction and pimozide, a potent neuroleptic with prolonged action used to prevent involuntary vocalizations of Tourette""s Syndrome. The butyrophenone antipsychotics have been demonstrated to have selective D2 dopaminergic receptor antagonism. (Goodman and Gilman""s The Pharmacological Basis of Therapeutics, Ninth Edition, Hardman, JG et al. (eds), McGraw-Hill, New York, 1996, p.406) Additionally, haloperidol has also been shown to have binding activity with sigma receptors (Seth et al, J Neurochem 70).
In the psychotic patient, following several days of neuroleptic administration, xe2x80x9cpositive symptomsxe2x80x9d such as agitation, hallucinations, delusions, disorganized thought tend to disappear and there are some effects onxe2x80x9cnegative symptomsxe2x80x9d as withdrawn or autistic patients can sometimes become more communicative. Overall, however, haloperidol and its chemical relatives are most noted for their treatment of xe2x80x9cpositive symptomsxe2x80x9d and have little effect on most catatonic patients. (Goodman and Gilman, Ninth Edition, p.407)
Dosing of haloperidol typically requires a 10 mg-16 mg loading dose followed by maintenance therapy of 12 mg-30 mg per day in divided doses. Dosing is individualized to allow patients to take the minimally necessary dose that alleviates symptoms (Harrison""s Principles of Internal Medicine, 13th ed., Fauci, AS et al. (eds.), McGraw-Hill, New York, 1994, p.2418). Because psychotic disorders are chronic diseases, and controlled studies have demonstrated relapses within 6 months in 60% of all patients, sustained therapy is recommended.
A prevalent side effect of both butyrophenone and phenothiazine (e.g. chlorpromazine) neuroleptics is the induction of extrapyramidal motor pathology. Extrapyramidal symptoms include parkinsonism, akathisia, dystonia and tardive dyskinesia. Such symptoms are apparent with both acute and chronic administration of neuroleptic drugs (Gill, HS et al., J. Clin. Psychopharm. 17(5):377-389(1997)). Dystonias typically appear within the first few days of therapy. These can manifest as either Parkinsonian-like tremors or as uncontrollable, spastic muscle contractions that produced anormal postures. Dystonic movements are typically slow, writhing movements that are transiently sustained. Ones that affect the eye muscles can be particularly disturbing as the patient loses ability to focus visually. In most patients coadministration of haloperidol with benzotropine or trihexyphenidyl (two anti-muscarinic agents) can reduce or alleviate the dystonic and Parkinsonian manifestations. Sustained, chronic use can induce tardive dyskinesia, a broad spectrum of hyperkinesias associated with exposure to neuroleptic drugs within 6 months of the onset of symptoms (although the patient has probably been on the drug for several years) which persists for 1 month after discontinuation of the neuroleptic agent. The most common movement manifestations of tardive dyskinesia involve repeated tongue protrusions and lip smacking. About 30% of all patients exposed to neuroleptic therapy develop some form of persistent movement disorder.
Development of extrapyramidal symptoms, and especially tardive dyskinesia as a consequence of long-term neuroleptic administration has been recognized for almost 4 decades. Tardive dyskinesia remains the most feared and disconcerting extrapyramidal side-effect of chronic treatment (Walters, VL et al., Schizophrenia Res. 28:231-246 (1997)). At the present time, therefore, prevention is best accomplished by intervening prior to the development of extrapyramidal symptoms (Walters et al. (1997)). Alternatively, although a variety of treatment therapies have been attempted in the treatment of tardive dyskinesia, none has become manifest as being successful in most patients (Egan, MF et al., Schizophrenia Bull. 23(4):583-609 (1997)).
From the above description of the manifestations of tardive dyskinesia and related motor dyskinesias, it is apparent that there is a compelling need for identifying alternative neuroleptic agents whose beneficial effects in the treatment of schizophrenia remain essentially undiminished from those in use currently, but which do not induce the symptoms of tardive dyskinesia. There further is a need for developing methods useful in screening pharmaceutical agents that are potential or candidate neuroleptics for their avoidance of the development of tardive dyskinesia. There is additionally a need for identifying molecular and cell biological bases for carrying out such methods. The present invention recognizes these deficiencies, and addresses their resolution.
The invention is based in part on the discovery that certain genes are differentially expressed in the brain striatum regions of animals treated with therapeutic levels of the common neuroleptic, haloperidol. These differentially expressed genes include novel and genes that, while previously described, have not heretofore been identified as haloperidol responsive.
Identification of the differentially expressed genes or gene fragments permits their use in identifying patterns of gene expression that produce the effects of tardive dystonia and similar dyskinesias when previously uncharacterized candidate neuroleptics are administered to a test system or to a test animal. Thus, the discovery allows for the identification of psychoactive agents, e.g. neuroleptic agents, which do not produce a pattern of differential gene expression characteristic of tardive dystonia and similar dyskinesias.
In various aspects, the invention includes methods of a method of identifying psychotropic agents, methods of diagnosing movement disorders, and methods of treating movement disorders. For example, in one aspect, the invention provides a method of identifying a psychotropic agent that does not induce a significant motor side effect by providing a test cell population comprising a cell capable of expressing one or more genes responsive to haloperidol, contacting the test cell population with the psychotropic agent; and comparing the expression of the gene in the test cell population to the expression of the gene in a reference cell population. An alteration in expression of the gene in the test cell population compared to the expression of the gene in the reference cell population indicates the psychotropic agent does not induce a significant motor side effect.
The invention in a further aspect includes a method of selecting a psychotropic agent appropriate for a particular subject. The method includes providing from the subject a cell population comprising a cell capable of expressing one or more genes one or more genes responsive to haloperidol, contacting the cell population with the psychotropic agent, and comparing the expression of the gene to the expression of the gene in a reference cell population. An alteration in expression of the gene in the test cell population compared to the expression of the gene in the reference cell population indicates the psychotropic agent is appropriate for the subject.
In a further aspect, the invention provides a method of diagnosing or determining susceptibility to a movement disorder in a subject. The method includes providing from the subject a cell population comprising a cell capable of expressing one or more haloperidol-responsive genes, and comparing the expression of the gene to the expression of the gene in a reference cell population that includes cells from a subject not suffering from a movement disorder. An alteration in expression of the gene in the test cell population compared to the expression of the gene in the reference cell population indicates subject has or is susceptible to a movement disorder.
Also provided are novel nucleic acids, as well as their encoded polypeptides, whose expression is responsive to the effects of haloperidol. Included are nucleic acids encoding two full-length human quaking homologs were identified. They are named human Qk5 and Qk7, for quaking splice variant 5, and human quaking splice variant 7, respectively.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In the case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description and claims.